Flexible current sensors are based on a flexible inductive coil which can be formed to create a closed path around a measured current carrying conductor. Voltage induced into the coil is proportional to the derivation of the total current flowing through the enclosed area. This principle of current measurement is well known as Rogowski principle or a Rogowski coil following the publication by W. Rogowski and W. Steinhaus in 1912. Flexible sensors are advantageous for current measurement in large size wires, difficult shape conductors and conductor groups.
Generally, a flexible current sensor has a form of a sensing cable equipped with a mechanical coupling system for either fixing or releasing the said sensor cable ends to and from the mutually closed position. The sensing cable comprises a sensing coil wound on a cylindrical flexible nonmagnetic core. The accuracy of flexible current sensors is significantly affected by stability sensor coil inductance. Beside winding density, the coil inductance is mainly affected by the accuracy and stability of the nonmagnetic core cross-sectional area.
Relevant solutions for Rogowski coil arrangements and their respective electronics can be found in following references:
U.S. Pat. No. 4,689,546 (Stephens et al) discloses an arrangement of plurality of classic single-coil flexible Rogowski sensors with a conventional metallic shield. Two individual sensor coils wound as bifilar are differentially interconnected and the output signal is conditioned with a differential amplifier in order to sense the power generator error current. This arrangement in the form of air-core current transformers disposed over conductors of a three-phase generator serves as a current monitoring equipment for generator control system.
U.S. Pat. No. 5,442,280 discloses fixed Rogowski coil arrangements on a printed circuit layout,
European Patent EP652441A1 discloses fixed Rogowski coil arrangements for installations with an earthed metal casing,
European Patent EP0834745A2 discloses an arrangement of a fixed Rogowski coil with high homogenity,
Japanese patent JP2000065866 discloses a multiple Rogowski coil arrangement for the measurement of current flowing through large structures,
UK patent application No. GB2332784A discloses flexible Rogowski coil arrangements comprising a sensor coil wrapped on a fixed support structure,
German patent application No. DE19811366A1 discloses flexible Rogowski coil arrangements optimized for repeated assembling on a power line,
UK patent No. GB2342783A discloses fixed Rogowski coil arrangements on a printed circuit layout,
U.S. Pat. No. 6,825,650B1 discloses arrangements of series of fixed Rogowski coils for current measurement in an electricity meter,
U.S. Pat. No. 6,313,623B1 discloses spatial arrangements of two Rogowski coils eliminating residual signals,
US pat. Application No. US2003/0090356A1 discloses fixed Rogowski coil arrangements on a printed circuit layout with an optic transmission path.
U.S. Pat. No. 7,847,543 B2 discloses a coil winding arrangement and an electrical shielding arrangement for flexible Rogowski coil improving accuracy and independency from electrical and external magnetic fields.
Principal linearity, lack of saturation of the nonmagnetic core and a wide frequency range are inherent properties of the Rogowski current sensors which continuously invoke demand for their further improvement and application oriented optimization. The accuracy of the state of the art flexible Rogowski current sensors is still insufficient for precision metering applications.
Therefore, the object of this invention is to provide a new and improved arrangement of a Rogowski flexible current sensor yielding significant accuracy improvement.